Vertebral arteries do not experience tensile force during manual cervical spine manipulation applied to human cadavers

ABSTRACT

Background

The vertebral artery (VA) may be stretched and subsequently damaged during manual cervical spine manipulation. The objective of this study was to measure VA length changes that occur during cervical spine manipulation and to compare these to the VA failure length.

Methods

Piezoelectric ultrasound crystals were implanted along the length of the VA (C1 to C7) and were used to measure length changes during cervical spine manipulation of seven un-embalmed, post-rigor human cadavers. Arteries were then excised, and elongation from arbitrary in-situ head/neck positions to first force (0.1 N) was measured. Following this, VA were stretched (8.33 mm/s) to mechanical failure. Failure was defined as the instance when VA elongation resulted in a decrease in force.

Results

From arbitrary in-situ head/neck positions, the greatest average VA length change during spinal manipulation was [mean (range)] 5.1% (1.1 to 15.1%). From arbitrary in-situ head/neck positions, arteries were elongated on average 33.5% (4.6 to 84.6%) prior to first force occurrence and 51.3% (16.3 to 105.1%) to failure. Average failure forces were 3.4 N (1.4 to 9.7 N).

Conclusions

Measured in arbitrary in-situ head/neck positions, VA were slack. It appears that this slack must be taken up prior to VA experiencing tensile force. During cervical spine manipulations (using cervical spine extension and rotation), arterial length changes remained below that slack length, suggesting that VA elongated but were not stretched during the manipulation. However, in order to answer the question if cervical spine manipulation is safe from a mechanical perspective, the testing performed here needs to be repeated using a defined in-situ head/neck position and take into consideration other structures (e.g. carotid arteries).

KEYWORDS:

• Spinal biomechanics
• spinal manipulation
• vertebral artery dissection
• cerebrovascular accidents
• stroke

Acknowledgements

The authors would like to acknowledge Drs. Ryan Carter and Bruce Symons for their clinical expertise delivering the manual procedures during testing.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Lindsay Gorrell: Conceptualization, Methodology, Formal Analysis, Investigation, Writing – Original Draft and Writing - Review and Editing. Andrew Sawatsky: Investigation, Writing – Review and Editing. Brent Edwards: Resources, Writing – Review and Editing. Walter Herzog: Conceptualization, Methodology, Resources, Writing – Review and Editing.

Data availability statement

The data that support the findings of this study are available from the corresponding author, [LG], upon reasonable request.

Additional information

Funding

This work was supported by the Canadian Chiropractic Research Foundation and the Alberta College and Association of Chiropractors. There was no involvement of either funding body in the study design, collection, analysis and interpretation of data, writing of the manuscript, and/or decision to submit the article for publication.